Let me tell you about a series of four terrific exercise DVDs under the umbrella title of Exhale Core Fuson: Pure Abs & Arms; Glutes & Thighs; Body Sculpt and Pilates Plus.

The Core Fusion practice was developed by Fred DeVito and Elisabeth Halfpapp, and is the featured mode of exercise at Exhale spas in the United States. The practice is a combination of the Lotte Berk Method, core conditioning, Pilates and yoga.

The exercises on the DVDs are extremely tough.

They’re very terrible.

You will cry for mercy.

The abdominal exercises, in particular, are insanely difficult.

But these exercises are effective, effective, effective.

Once you see your stomach sucking in, your thighs getting long and lean and your calves looking slim and muscular, you will shriek for joy and want to put yourself through the same torture again.

It’s a great confidence booster, too, as you find your strength and ability improving.

The instructors’ philosophy concentrates on proper form over the number of repetitions. You’ll hear that over and over from them — it’s much more important to do a few exercises in the proper form than many in sloppy form.

If done properly, each and every exercise will work your core muscles in addition to the area being worked.

Each DVD is divided into five 10-minute sections. The sections can be done individually (which I do, adding one or two to the end of cardio workout), or as complete workouts on their own.

All four, with the exception of Glutes & Thighs, finishes with a stretching segment.

• Pilates Plus contains what I consider the most varied workout of all the DVDs.

- It starts with a challenging, and very effective, upper-body core workout, which features holding the plank position and doing pushups. I credit this segment for getting my upper body and arms strong enough to do an entirely different workout with nine sets of eight pushups (I’ll write about this one another time.)

- Thigh and gluteus core has a person on their knees on the ground, leaning back and forth (a killer on the thighs), then moving to an all-fours position and lifting up the legs for the glutes (also killer.)

- Flat back/round back core is a unique segment, unlike any type of exercise I’ve done before. Sitting on the ground and lifting your stomach muscles, the legs are lifted in a different variety of ways.

- Pure core is the most insanely hard abdominal exercises I’ve ever done. Fred and Liz don’t do crunches. They lift up their head and neck and keep it in one position, as the legs are lifted in different positions and the arms are moved in different ways.

You will feel a burn in your stomach that will make you sure it’s on fire.

• Pure Abs and Arms tackles these two areas fiercely and effectively. Segment one is arms with weights, segment two is arms with the provided stretch band, and segments three and four work on abdominals.

Segment three does killer abdominal work with the stretch band, while segment four involves putting legs up in the air, and using the band extended around them, or a yoga block or towel placed between them for more effective ab work.

I’m crediting segment four for helping to tone up the muscles of my lower back, as some back power is needed to lift and move the legs and keep the abdominals in the required position.

The first two segments are turned-out thigh and parallel thigh, done with the assistance of a chair. Turned-out thigh involves putting your feet in a small V, lifting them off the group and then doing deep-knee bends. Parallel thigh is the same, but with feet forward and together. Feel the burn in your thighs and calves.

The next two segments are gluteal toners. The first, standing, involves holding the chair lightly and pushing back one’s leg in “ballet”-type points.

The final challenge is pretzel, which looks so impossible I haven’t even tried it. This position involves is sitting on the ground with legs extended to the back in a stretch position and lifting the legs.

• Body Sculpt is a varied workout, beginning with an upper-body sculpt using weights; a standing thigh-sculpt workout using exercises similar to the ones featured on Glutes and Thighs; a gluteus sculpt which involves kneeling over a chair and lifting the legs back and up (very difficult); a killer abdominal sculpt section and a final stretch sculpt.